Accelerometers are used to convert gravity-induced or motion-induced acceleration into an electrical signal that can subsequently be analyzed. Accelerometers are used in widely diverse applications including automobile air bag and suspension systems, computer hard disc drives, detonation systems for bombs and missiles, and machine vibration monitors. Accelerometers are also useful in portable devices such as wireless telephones, for example in order to cause a device to power up when the device moves sufficiently to indicate that a person has picked up the device. Wireless devices such as wireless phones operate using small batteries, and therefore it is important for every component of a wireless device to consume as little power as possible, including not just an accelerometer, but also the circuits used to evaluate data from an accelerometer.
The simplest accelerometer is only able to measure one component of the acceleration vector, but more complex accelerometers are equipped to measure all three components of acceleration, in which case the accelerometer is called a 3-axis or triaxial accelerometer. The output signal from, an accelerometer may be digital, or the output signal may be converted from analog to digital.
It has been well known for many decades that a typical accelerometer will include a “proof mass” (sometimes called a “seismic mass”) which is attached to a spring, and the output signal will then be determined by the position of the proof mass. This process of producing an output signal is accomplished differently in different accelerometers, which may be potentiometric, or capacitive, or inductive. In recent years, other types of accelerometers have been developed which, for example, do not require and proof mass at all. The minimum size of an accelerometer has been gradually reduced over the years, as Micro Electro-Mechanical Systems (MEMS) technology has improved. Some MEMS-based accelerometers do not even require any moving parts.
The electrical output signal from an accelerometer must be processed in order to yield conclusions about the acceleration experienced by the device that houses the accelerometer. According to typical prior art techniques, the digital output signal from a triaxial accelerometer will be processed with full accuracy by an elaborate and energy-demanding process that involves, for example, a combination of high-pass and low-pass filtering, decimation, and calibration. It would be very useful if this prior art technique could be complemented by a less energy-demanding technique for use when less accuracy is required. This would be especially useful in portable wireless devices, which usually have very limited power capabilities.